1. Field of the Invention
The invention relates to a black body radiator comprising a body which is heatable by means of a heating device and has temperature sensors, and a radiating surface.
2. Description of the Prior Art
For calibrating infrared measuring devices or meters black body radiators are employed which are introduced into the beam path of the measuring device. Usually, black body radiators are metallic bodies which are heated in various manners. All black body radiators emit the radiation in a limited space angle, at the most into half space. This means that the greater part of the heated body of the black body radiator is not employed for the actual purpose. To minimize the necessary heating power, the unemployed portions are insulated by conventional technique, for example by means of mineral wool, to avoid heat loss. A disadvantage here is that for good thermal insulation the radiator necessarily becomes large and on the other hand when a small structure is employed the heat losses become greater, in particular, it is difficult to integrate a calibrating radiator into a measuring device because a small structure leads to high heat losses which can disturb the actual measuring process particularly in the case of infrared measuring devices. On the other hand, good thermal insulation again results in a large and thus unwieldy device.
Usually, the electrical heating is effected via heating wires which are laid in the radiating body with good thermal contact. This results in a spatially initially inhomogeneous heating which should be made uniform by the heat flow in the body before the heat reaches the radiating surface so that at the latter a homogeneous heat distribution ensures a homogeneous radiation. This is achieved firstly by a large packing density of the heating wires and secondly by a large material thickness between the heating wires and the radiating surface; however, because of the expenditure and larger dimensions involved and the resulting additional weight both of these measures must be considered disadvantageous.
U.S. Pat. No. 4,387,301 discloses a surface radiator with structured surface with which radiation patterns for thermal cameras are generated. Furthermore, from DE 33 46 456 C2 a black body radiator is known which comprises a galvanically coated surface serving as thermoelement for measuring a temperature. From U.S. Pat. No. 4,184,066 a surface radiator is moreover known in which special ceramic heating elements are employed. In addition, the heating element is surrounded by a housing which has a hood-like cover by which the surface radiator is shielded from external light which would otherwise impinge on the surface radiator.